I think zytox is incorrect, at least in PHP 5.0.4.It returns null, but you have to be careful with your comparison operators.

As an example:<?phpunset($null);if (pg_connection_status($null)===PGSQL_CONNECTION_OK) echo 'this is not called';if (pg_connection_status($null)==PGSQL_CONNECTION_OK) echo 'this is called because NULL==0 is true';?>